Many contemporary electronic devices have the capability to connect with external or peripheral audio devices. For instance, mobile telephones, tablets, laptop computers, mp3 players and the like are examples of electronic devices that are operable with peripheral audio devices such as a headset, for example, that is external to and distinct from the electronic device. A peripheral device such as a headset may typically comprise mono or stereo speakers for audio playback and possibly a microphone for voice communication.
Such external peripheral audio devices are often connected via a mating connector such as a plug and socket arrangement. For instance, many audio peripherals such as headsets have a jack plug such as a 3.5 mm jack plug for connection to a suitable jack socket on the host electronic device. A well-known arrangement for a jack plug and its associated socket is TRRS (Tip-Ring-Ring-Sleeve), which has four contacts for left audio, right audio, microphone, and ground. In one known arrangement, the tip (T) and first ring (R1) are used for left (L) and right (R) audio, for example left and right loudspeakers, with the second ring (R2) and sleeve (S) used for the microphone (M) and ground return (G) respectively. It will be appreciated that different arrangements for the left and right audio, microphone, and ground contacts are also possible. This provides for transfer of two channels of analogue audio data from the host device to the peripheral and transfer of a single channel of analogue audio data from the peripheral microphone to the host device. Other connectors allow for the transfer of digital data between the peripheral device and the host device. For example, USB connectors are well known and comprise a plurality of pins for the transfer of digital data. The Lightning® connector produced by Apple Inc. is another example. Such digital data connections require configuration, for example to identify the peripheral device and load appropriate drivers for that peripheral device, to assign an address to the peripheral device, and so forth. In the USB standard, such a process is known as enumeration.
In order to save power, a peripheral device may comprise a mechanism to enable it to be switched off, or placed in a low-power state. For example, in one arrangement, the peripheral device may comprise a power button which can be actuated by a user to switch the peripheral device off. In more complicated arrangements, the peripheral device may be switched off or powered down automatically, upon detection of an event such as a voice command or a period of inactivity. The peripheral device may draw power from the host device via the connection, and thus power is saved in the host device by deactivating the peripheral device when not in use.
A problem occurs when such a peripheral device is connected to a host device via a digital data connection (such as a USB connection), and is powered down or switched off without decoupling the connector of the peripheral device from the connector of the host device. Currently, designers are faced with two options upon the peripheral device being switched off: pull down the digital data connection between the host device and the peripheral, or maintain the digital data connection. The problem with pulling down the digital data connection is that the mechanism by which to detect power on of the peripheral device is similarly lost. The user can no longer use the power button on the peripheral, as the transfer of data indicating power on takes place via the digital data connection. Thus present devices utilize the second option, and maintain an active digital data connection between the host device and the peripheral device, even when the peripheral device is otherwise powered down. However, the active digital data connection consumes power in the order of tens of milliamps. Particularly in the field of mobile electronic devices, power consumption is an important consideration and should be reduced to the extent possible. Therefore the second option also has disadvantages.